In conventional technology, machine tools are known that cause relative movement of a tool with respect to a workpiece to perform machining such as cutting. Among such machine tools, numerically-controlled machine tools are known that specify the tool path with a coordinate or the like of a predetermined axis and perform machining while moving the tool automatically with respect to a workpiece. By moving at least one of the workpiece and the tool, the relative position of the tool with respect to the workpiece can be changed. As a method of changing the relative position of the tool with respect to the workpiece, control is known in which the workpiece or the tool is rotated along a rotary feed axis about an axis line, besides control of moving the workpiece or the tool along a linear motion axis.
The axis line of the rotary feed axis for relative movement of the tool with respect to the workpiece can be set parallel to the linear motion axis, for example. In other words, rotary movement of the workpiece or the tool can be caused about the axis line parallel to the linear motion axis. Examples of the machine tool in which the axis line of the rotary feed axis is set parallel to the linear motion axis include a machine tool which rotates a table in the B-axis direction about an axis line parallel to the Y-axis and a machine tool which rotates a table in the A-axis direction about an axis line parallel to the X-axis.
In such machine tools in which the axis line of the rotary feed axis is set parallel to the linear motion axis, a table can be supported by arranging a supporting member at one end or both ends in the axis line of the rotary feed axis. However, when one end in the axis line of the rotary feed axis is supported, there is a problem that the support stiffness for the table decreases. When ends on both sides in the axis line of the rotary feed axis are supported, two supporting members are called for, and there is a problem of a device supporting the table being large in size. Thus, a machine tool is proposed in which an axis line of a rotary feed axis is inclined with respect to a linear motion axis.
In Japanese Laid-open Patent Publication No. 61-79508A, a numerically-controlled machine tool is disclosed including a table which rotates about a central axis of rotation inclined by 45 degrees with respect to the horizontal direction, wherein a table itself rotates about another central axis of rotation which intersects with the central axis of rotation at a 45-degree inclination. The publication discloses that, upon performing oblique machining on a workpiece, the angular position of rotation of an inclined rotation table and the position of a tool are obtained by a predetermined formula, and the machine tool is positioned in the position to perform machining.